Force measuring apparatus with cumulative ranges of measurment



March 30, 1965 F. E. SACHERS 3,175,393

FORCE MEASURING APPARATUS WITH CUMULATIVE RANGES OF MEASUREMENT FiledSept. 17, 1962 4 Sheets-Sheet 1 E u 11 INVENTOR.

FRITZ E. SACHERS ZBY I X 4770 EYS.

March 30, 3965 F. E. sAcHERs 3,175,393

FORCE MEASURING APPARATUS WITH CUMULATIVE RANGES OF MEASUREMENT FiledSept. 17, 1962 4 Sheets-Sheet 2 INVENTOR FRITZ E. SACHERS ATTORN .5.

March 1965 F. E. SACHERS 3,175,393

FORCE MEASURING APPARATUS WITH CUMULATIVE RANGES 0F MEASUREMENT FiledSept. 17, 1962 4 Sheets-Sheet 3 OFF POWER DEMAG.

INVENTOR.

FRITZ E. SACHERS ATTOI? Y5.

March 30, 1965 F. E. SACHERS FORCE MEASURING APPARATUS WITH CUMULATIVERANGES OF MEASUREMENT 4 Sheets-Sheet 4 Filed Sept. 17, 1962 INVENTOR.

FRITZ E. SACHERS ATTOR/V 5,

United States Patent M 3,175,393 FORCE MEASURENG APPARATUS WITH CUMU-LATEVE RANGES it)? MEASUREMENT Fritz E. Sachers, New York, N.Y.,assignor to Aero-Chatillon Corporation Filed Sept. 17, 1962, Ser. No.224,190 3 Claims. (Cl. 73-134) The invention relates to force measuringapparatus and has special application to the measurement of dynamic andstatic torque as by absorption dynamometers but is applicable to otherforms of force measuring devices as well.

The principal problem to the solution of which the present invention isaddressed, has arisen in connection with absorption dynamometers of thetype employing an electromagnetic brake, and the principal embodiment ofthe invention which will be particularly described herein, will disclosethe application of my invention to such type of dynamometer. In oneprevious commercial form of such apparatus, the electromagnetic brakeoperates in conjunction with what are known as torque cells containingtorsion springs arranged to resist movement of the stator of the brake.In order to cover the operating range of the brake, it was necessary tomanually interchange torque cells of different capacities, each of thedifferent torque cells utilizing torsion springs of different capacitiesin order to cover different portions of the complete operating range.When using such apparatus to test motors of unknown torque, itfrequently is necessary to resort to trial and error to determine theproper size of torque cell to be used. It has been a principal object ofmy invention to avoid the necessity for employment of such trial anderror methods, and also to avoid the need for manual interchange oftorque cells. Accordingly the force measuring apparatus embodying myinvention is capable of automatically shifting the force measurementbetween two or more separate torque systems in such a manner that thefirst torque system which is brought into play will actuate the secondand, as the force continues to increase, a third torque system may beactuated, and so on. The forces of the springs or other means of eachtorque system are cumulative so as to provide successive ranges ofincreasingly higher force measurement without requiring any specialadjustment or attention by the operator. The successive ranges may beshown upon a single dial in which the indicating pointer passes from onerange of measurement to the next. According to a preferred form of myinvention as applied to the electromagnetic brake type of absorptiondynamometer, the apparatus is completely reversible for measurement oftorque in either the clock- Wise or counterclockwise direction ofrotation.

In its general arrangement my force measuring apparatus comprises amember mounted to turn about a pivot axis, means for applying torque tosuch member from an external source (such as an electrical motor,hydraulic motor, turbine, air motor, or other unit to be tested), meansfor resisting the turning movement of the aforesaid member about thepivot axis, and means for indicating the extent of such turningmovement. An essential feature of such apparatus resides in theparticular construction of the aforesaid means for resisting the turningmovement of the member, for example, the turning movement of the memberrepresented by the stator of the electromagnetic brake. Such resistingmeans includes a plurality (two or more) of torque elements, eachseparately loaded against turning movement, and a lost motion clearancebetween successive torque elements. The stator or other member ispermitted to move initially over a range in which its movement is3,1753% Patented Mar. 30, 1965 resisted solely by a first one of thetorque elements until at the end of the lost motion interval of thedriving connection between said first torque element and a succecdingtorque element, the movement of the member is resisted by both the firstand succeeding torque elements over a second range of such movement.Thus the action of the two torque elements is cumulative in the sensethat both such elements operate together through the second range. Athird or any other number of additional ranges may be employed asdesired, using a lost motion driving connection between the torqueelements of the successive ranges.

Referring to the drawings in which I have illustrated the best modecontemplated by me for carrying out my invention:

FIG. 1 is a side elevational view, partly in central vertical section,of an apparatus constructed in accordance with my invention.

FIG. 2 is a detail horizontal sectional view taken as indicated at 2-2in FIG. 1.

FIG. 3 is a diagrammatic exploded perspective view showing the threetorque elements of FIGS. 1 and 2.

FIG. 4 is a perspective View of an absorption dynamometer embodying theapparatus of FIGS. 1 and 2 coupled to a motor that is to be tested.

FIG. 5 is a perspective view of the dynamometer of FIG. 4 with the outercase removed, viewing the mechanism from the rear.

In the preferred embodiment shown in the drawings, a frame 1 fixed to abase 2 includes bearings 3, 4 and 5 in which are supported the rotatingelements of the apparatus including an electromagnetic brake indicatedgenerally at 6, and the series of discs '7, 8 and 9 comprised in thetorque elements of the device. The pivot axis of the several elementshaving rotative movement is indicated at AA. The input shaft 10 of thedynamometer is suitably coupled to the motor or other unit 11 to betested. Freely mounted on the input shaft It) is a bracket 12 in whichis provided a recess 13 to receive the stator 14 of the electromagneticbrake 6. Indicating means such as the pointer 15, extends from bracket12 over the top of an indicating dial 16. (In FIG. 5 pointer 15 is shownas extending from a connection at the rear of the electromagnetic brake,in this respect being a modification of the structure indicated inFIG. 1. Input shaft 10 is keyed to the rotor of the electromagneticbrake 6 which may be of any well known construction such as thecommercially available electromagnetic hysteresis or magnetic particlebrake. Fixed to the stator 14 of the brake is a bracket 17 having asleeve 18 surrounding shaft 10, sleeve 18 being carried in bearings 4 ofthe supporting frame 1. Sleeve 18 is fixed to an other sleeve 19 as bymeans of a set screw 2t), sleeve 19 being freely rotatable with respectto shaft 19. Keyed to sleeve 19 is the disc 7 of a first torque element.A metal tape 21 is wrapped around the lower half of disc 13 and affixedthereto as by means of a screw 22. The ends of tape 21 are secured tocoil springs 23 (cf. FIG. 3) which in turn are secured to a plate 24fixed to a pair of mounting rods 25 extending upwardly from the frame 1.Mounting screws 26 and attached spring holders 27 provide means forcalibrating the springs to the desired initial tension.

In line with shaft It! is a shaft 23 mounted in frame 1. Freely mountedon shaft 28 are the discs 8 and 9 of a second and third set of torqueelements, the construction of which is substantially similar to that ofthe one already described. In the construction shown the springs 2 ofthe second torque elements are heavier than the springs 23 of the firsttorque element, and the springs 30 of the third torque element areheavier than the springs 29.

With reference to FIG. 2, I shall now describe the lost motion drivingconnection between the discs 7, 8 and 9 of the successive torqueelements. This driving connection may conveniently be secured by aseries of cooperating drive pins. In the construction shown, a singlepin 31 extends rearwardly from the upper portion of disc 7. A pair ofpins 32 extend from the opposite face of disc 8 and are mounted thereinat the same radial distance from the pivot axis AA as in the pin 31 ofdisc 7 so that as disc 7 rotates in one direction or the other, the pin31 will engage one of the pins 32 in a manner to drive disc 8 from disc7. Similarly, a single pin 33 extends rearwardly from disc 8 forengagement with either of the pins 34 extending from the opposite sideof disc 9 whereby after the clearance between pin 33 and one of the pins34 has been taken up, disc 9 will be driven from disc 8.

The clearances between pins 31 and 32 on the one hand, and pins 33 and34 on the other, are predetermined to permit movement of the stator 14of the brake initially over a range in which its movement is resistedsolely by the first torque element until at the end of the lost motioninterval of the driving connection between the first torque element andthe succeeding torque element, the movement of stator 14 is resisted byboth the first and succeeding torque elements over a second range ofsuch movement. The indicating dial 16 has indicia 35 calibrated to theseveral ranges, in this case three ranges for a clockwise rotation andthree ranges for counterclockwise rotation. As the pointer moves fromthe zero position shown at the top of FIG. 4, it will pass into orthrough the first range a in which movement is resisted solely by thefirst torque element or cell. Then as the load increases, the pointerwill enter the second range b in which the movement of the stator 14 isresisted by the first and second torque elements or cells. Similarly, asthe load increases still further, the pointer will pass into the rangewhere we have the cumulative resistance of the three torque units. Itwill be understood that the pairs of springs 23, 29 and 30 wouldordinarily be placed under initial tension and that upon rotation of thediscs the action will cause one spring of a pair to shorten as the otherlengthens so that the net spring loading will be the algebraic sum ofthe increased tension on the one spring and the decreased tension on theother.

Suitable means may be provided for measuring and indicating the speed inr.p.m. of the input shaft or of the equal speed of the output shaft ofthe motor or other unit being tested; for example, a standardphotoelectric tachometer, the indicating scale of which may convenientlybe located as shown at 36 in FIG. 4. In FIG. the photoelectric beam isprojected from a conventional source as at 37, the beam passing throughan aperture 38 in the shaft and being interrupted intermittently by thesolid portion of the shaft as the latter rotates. Conventional meanssuch as the electronic power unit 39, FIG. 5, may be used to activatethe electrical coil of the electromagnetic brake 6 through a torquecontrol potentiometer 40 which may conveniently be operated by a knob 41on the front panel of the dynamometer. The brake 6 may be of either thehysteresis type or magnetic particle type, both of which are well knownand available commercially.

Operation In operation the dynamometer is attached to a suitable sourceof electric power and the motor 11 to be tested likewise is connected toits appropriate power source and provided with a mounting on the base 2of the instrument in the manner indicated in FIG. 4, its shaft beingconnected to input shaft 10, FIG. 1, by means of a suitable flexiblecoupling. The power is then turned on and a suitable time allowed forthe circuit to warm up, after which the motor to be tested is energized.

Next the operator turns the torque control knob 41 until the desiredtorque is indicated by the pointer 15 against the dial 35. When thistorque is reached, the operator reads the r.p.m. on dial 36 or measuresthe rpm. by the use of a separate tachometer as desired. In my preferredconstruction the speed indicator is formed as an integral part of theinstrument as shown.

In operation, the motor under test drives the rotor (not shown) of thebrake. The magnetically coupled stator 14 attempts to follow the rotorbut is restricted by the action of one or more of the sets of springs23, 29 and 30. The magnitude of the reactive force exerted by thesprings is transmitted to the pointer 15 and indicated by the positionof the pointer on the dial 35 which may, for example, be calibrated ininch ounces or inch pounds. The corresponding tachometer reading maythen be used to translate the force into horsepower in accordance wihstandard prony brake procedure.

As the dynamometer measures the increasing reactive force, the firsttorque system 7, 21, 23 actuates the second 8, 21, 29, and, as the forcecontinues to increase, the third torque system 9, 21, 30 is actuated,thus accumulating the forces of the three sets of springs. This multipletorque system may be used not only in conjunction with anelectromagnetic brake but also in conjunction with a conventional pronybrake, an hydraulic brake, or other desired forms of braking mechanisms.Further, the multiple torque system may be adapted to use with weighingscales.

Operation of the electromagnetic brake itself is well known and need notbe particularized, except for a general statement. Assuming a brake ofthe hysteresis type, we have an input shaft 10 with a disc attached thatis rotated within the stator 14. Passing current through the statorwindings creates a hysteresis effect which tends to restrain the rotor.The amount of current supplied to the stator windings determines themagnitude of the restraining force. The stator is pivoted in ballbearings and attempts to follow the rotation of the input shaft but isrestrained by a system of calibrated balanced springs. A slip isthereafter introduced between the input and stator which is measured bythe spring balance. Energy produced by the motor is converted to heatand dissipated by the brake. Operation of the photoelectric tachometeris conventional. A beam of light is transmitted from the source 37 to aphotoelectric cell. The beam is interrupted as the shaft rotates in themanner already described. An amplifier shapes the resultant pulse,regulates and converts it to a current pulse which is then averaged bythe meter circuit.

The terms and expressions which I have employed are used in adescriptive and not a limiting sense, and I have no intention ofexcluding equivalents of the invention described and claimed.

I claim:

1. In force measuring apparatus comprising a member mounted to turnabout a pivot axis, means for applying torque to said member from anexternal source, means for resisting turning movement of said memberabout the pivot axis, and means for indicating the extent of suchturning movement, the construction in which the resisting means includesa plurality of torque elements each separately loaded against turningmovement, and a. lost motion driving connection between successivetorque elements having a predetermined lost motion clearance betweensuccessive torque elements to permit movement of said member initiallyover a range in which its move-- ment is resisted solely by a first oneof the torque elements until at the end of the lost motion interval ofthe driving connection between said first torque element and asucceeding torque element the movement of said member is resisted byboth the first and succeeding torque elements over a second range ofsuch movement.

2. In force measuring apparatus comprising an electromagnetic brake, aninput shaft arranged to drive the rotor;

of said brake and the stator of the brake being mounted for limitedrotative movement around the axis of said input shaft, means forresisting such rotative movement of the stator, and means for indicatingthe extent of such rotative movement, the construction in which theresisting means includes a plurality of torque elements each separatelyloaded against turning movement, and a lost motion driving connectionbetween successive torque elements having a predetermined lost motionclearance between successive torque elements to permit movement of saidstator initially over a range in which its movement is resisted solelyby a first one of the torque elements until at the end of the lostmotion interval of the driving connection between said first torqueelement and a succeeding torque element the movement of said stator isresisted by both the first and succeeding torque elements over a secondrange of such movement.

3. In force measuring apparatus comprising an electromagnetic brake, aninput shaft arranged to drive the rotor of said brake and the stator ofthe brake being mounted for limited rotative movement around the axis ofsaid input shaft, means for resisting such rotative movement of thestator, and means for indicating the extent of such rotative movement,the construction in which the resisting means includes a plurality ofdiscs mounted for limited rotative movement about a common axis, a lostmotion driving connection between successive discs having apredetermined lost motion clearance between successive discs, and springmeans arranged to load each of said discs separately, the predeterminedlost motion clearance between successive discs permitting movement ofsaid stator initially over a range in which its movement is resistedsolely by the spring means associated with a first one of said discsuntil at the end of the lost motion interval of the driving connectiongbetween said first disc and a succeeding disc the movement of the statoris resisted by the springs associated with the first and succeedingdiscs over a second range of such movement.

References Cited by the Examiner UNITED STATES PATENTS 2,043,147 6/36Bestoso 73-135 2,674,121 4/54 German 73-397 X 2,744,409 5/56 Wintle eta1. 73-434 2,785,568 3/57 Schultz et al. 73134 FOREIGN PATENTS 571,2138/45 Great Britain.

r RECHARD C. QUEISSER, Primary Examiner. J

JOSEPH P. STRIZAK, Examiner.

1. IN FORCE MEASURING APPARATUS COMPRISING A MEMBER MOUNTED TO TURNABOUT A PIVOT AXIS, MEANS FOR APPLYING TORQUE TO SAID MEMBER FROM ANEXTERNAL SOURCE, MEANS FOR RESISTING TURNING MOVEMENT OF SAID MEMBERABOOUT THE PIVOT AXIS, AND MEANS FOR INDICATING THE EXTENT OF SUCHTURNING MOVEMENT, THE CONSTRUCTION IN WHICH THE RESISTING MEANS INCLUDESA PLURALITY OF TORQUE ELEMENTS EACH SEPARATELY LOADED AGAINST TURNINGMOVEMENT, AND A LOST MOTION DRIVING CONNECTION BETWEEN SUCCESSIVE TORQUEELEMENTS HAVING A PREDETERMINED LOST MOTION CLEARANCE BETWEEN SUCCESSIVETORQUE ELEMENTS TO PERMIT MOVEMENT OF SAID MEMBER INITIALLY OVER A RANGEIN WHICH ITS MOVEMENT IS RESISTED SOLELY BY A FIRST ONE OF THE TORQUEELEMENTS UNTIL AT THE END OF THE LOST MOTION INTERVAL OF THE DRIVINGCONNECTION BETWEEN SAID FIRST TORQUE ELEMENT AND A SUCCEEDING TORQUEELEMENT THE MOVEMENT OF SAID MEMBER IS RESISTED BY BOTH THE FIRST ANDSUCCEEDING TORQUE ELEMENTS OVER A SECOND RANGE OF SUCH MOVEMENT.